Pump pistons for use in mud or slush pumps are virtually expendable. Their lives are relatively short compared with their mating components such as liners or cylinders. Typically, a liner often runs twice or even longer than its mating piston.
The pistons moving back-and-forth within the liners or the cylinders will suffer damages mainly from two sources. The first one would be heat generated during the movements. Generally, the heat degrades piston's seal or ring, which usually is made of elastic materials such as rubber or polyurethane, has a greater diameter than the inner diameter of the cylinder or the liner so that leakage could be prevented. Thus, during the movements, the piston is consistently scrubbing said wall, from which the heat is generated.
The second source is scratching to the piston by debris. The debris may be foreign materials leaked from the liner or the cylinder, or detached materials from the wall of the liner/cylinder, or the piston. The scratching is especially damageable to the seal or the ring, since they are typically made of relevant soft materials comparing to the wall and other portions of the piston.
In order to reduce the damages to the pistons, they are equipped with flushing systems, wherein liquids are pumped into the pistons and carrying away both the heat and the debris.
For example, WO 2009/051493 discloses a piston head have a fluid supply mean 52 passing through the piston head to an annulus between a first and a second projection of said head. Especially, both projections are designed with angles so that water or oil may be forced into the annulus, flush away the heat and the debris, and substantially flow into the cylinder's working space.
For another example, U.S. Pat. No. 3,720,140 discloses a piston that has a fluid supply carried through flexible conduit which is threadedly secured into a piston rod, communicating with passageways. The passageways in term communicate with an annular groove in the periphery of a flange of the piston. Similar to that disclosed in WO 2009/051493 the liquid carrying the heat and the debris flows into the cylinder's working space.
To further protect the pistons from damages caused by the heat and the debris, there is a need for a more efficient system to exchange the heat and flush away the debris. There is also a need for a system that provides more uniformly distributed exchanging and flushing effects.